1. Field of the Invention
The present invention relates to a high-capacity LiMn.sub.2 O.sub.4 compound used for non-aqueous electrolyte lithium ion battery, more particularly, to a method for preparing LiMn.sub.2 O.sub.4 intercalation compound doped with Li and Co ion, which comprises the following steps of : synthesis of spinel type LiMn.sub.2 O.sub.4 powder ; dissolving and treating LiMn.sub.2 O.sub.4 powder in the solution to adsorb Li and Co ion ; and thermal treatment of said LiMn.sub.2 O.sub.4 to obtain LiMn.sub.2 O.sub.4 doped with Li and Co ion.
2. Description of Prior Art
Technologies regarding camcorder, cellular phone and note book PC etc. have been developing rapidly according to the development of electronics, communication and computer industries. The secondary battery which can be used continuously by recharging has been required for the electric power of such instruments. Especially, lithium ion batteries in which lithium ion can be reversibly charged and discharged has been researched for its high voltage(3.about.4 V) and high energy density(about 100 Wb/Kg).
In a lithium ion battery, compounds which can charge and discharge lithium ions are used as the materials for cathode and anode. Especially, compounds of transition metal oxide, such as, LiCoO.sub.2, LiNiO.sub.2, LiMn.sub.2 O.sub.4 are chiefly regarded as good cathode materials with respect to electric power, energy density and safety. Among them, LiMn.sub.2 O.sub.4 has been regarded as desirable material in the point of the price of material and the effect to environment.
However, the application of LiMn.sub.2 O.sub.4 to lithium ion battery has some handicaps due to the decline of discharging capacity by the result of repeated charging and discharging. One of the main reason why the capacity is declined by repeated charging and discharging has been regarded as the dissolution of Mn.sup.+3 ion in LiMn.sub.2 O.sub.4 to electrolyte and the structural unstability according to Jahn-Teller transition(J. Electrochem Soc. 143(1996) 2204).
To solve the above problems, the technology of doping metal salts, such as, Co, Cr and Ni salt to LiMn.sub.2 O.sub.4 has been disclosed. For example, the method for preparing LiMn.sub.2 O.sub.4 doped with metal salts comprising i) mixing lithium carbonate, manganese acetate and cobalt oxalate, ii) prethermal treatment of mixture at 600.degree. C. for 6 hours, and iii) thermal treatment at 750.degree. C. for 3 days in air was disclosed in J. Electrochem. Soc., 143(1996) 178. Further, the method for LiMn.sub.2 O.sub.4 doped with metal salts comprising i) mixing lithium salt, manganese salt and cobalt salt, and ii) thermal treatment at 800.degree. C. for 6 hours was disclosed in J. Electrochem Soc., 143(1996) 3590. However, the thermal treatment at high temperature in above methods causes the handicaps for the application to preparing doped LiMn.sub.2 O.sub.4 used for cathode material in lithium ion battery.